A dual clutch transmission of a vehicle typically utilizes two manual shift transmissions in a single housing to drive the wheels of a vehicle with different gear ratios or stages. A conventional dual clutch transmission generally contains two independent clutches that are normally open or released, and further includes at least one input shaft, and at least one output shaft operably coupled with each other. Each of the two clutches is coupled to its corresponding input shaft to drive an output shaft with selected gear ratios.
In order to perform the gear shifting process, the dual clutch transmission further includes a gear shift actuating device which is driven by an actuator such as an electric motor. According to the dual clutch transmission systems known in the art, the gear shifting devices typically include a drive shaft, a shift finger for the gear engaging operation, and elements designed particularly for disengaging operations of the gears. For example, as illustrated in FIGS. 3a and 3b, a conventional gear shifting device for double-clutch transmissions known in the art uses shift frames 301, 302, 303, and 304 to move corresponding shift members to engage with the gears assigned thereto, and further includes a drive shaft 315 (only a portion shown in FIG. 3a) with a shift finger 316 and a plurality of disengagement cams 316a formed on the drive shaft 315 for the engagement and disengagement operation of the gears, respectively. As shown in FIGS. 3a and 3b, each shift frame (301, 302, 303, and 304) includes inner cam groove 306 of complex contour combined with a generally rectangular cam groove and two opposing circular cam grooves formed at two opposite sides of the rectangular groove. As shown in FIG. 3c, which is a sectional view taken along the line A-A in FIG. 3b, the cam groove 306 of each of the shift frames 301-304 has the same width 331a, the shift finger 316 has a width 332a between two opposite sides (shift finger contact sides), which width is smaller than width 331a of the shift frame.
In order to shift and engage a selected gear, the drive shaft 315 is first axially displaced so as to align the shift finger 316 with the shift frame 301-304 (for example, shift frame 304 as shown in FIG. 3c) of the target gear. The drive shaft 315 is then rotated by actuator, and the shift finger 316 pushes the selected shift frame by rotational cam contact of the shift finger 316 against the two opposite rectangular sides of cam groove 306 of the selected shift frame, and as a consequence, the selected shift frame (e.g., shift frame 304) for the target gear moves in lateral direction to predetermined distance, namely, either distance 332b to set one gear ratio or distance 332c to set a different gear ratio according to the design of the transmission. On the other hand, in order to release or disengage one or more non-target gears, the drive shaft 315 is again axially moved until the shift finger 316 is aligned with the shift frame (301, 302, 303, or 304) for the gear to be released, and one of the multiple disengagement cams 316a of the drive shaft 315 rotates to a releasing direction and pushes the cam groove 306 of the shift frame upon rotation of the drive shaft 315, and the shift frame for the gear to be released moves in lateral direction by a predetermined distance to release the releasing gear.
As described above, this conventional gear shifting device requires complex cam parts to be manufactured with precision, such as shift frames 301-304 with complex cam grooves produced in high precision and accuracy, shift finger 316 with precise cam contour, and multiple disengagement cams 316a with precise cam contour. Thus, this shifting device requires a complex production process and a high manufacturing cost.
Moreover, as shown in FIG. 3a, the drive shaft 315 (only a portion shown in FIG. 3a) extends in a direction perpendicular to the shift frames 301-304, and as a consequence, also perpendicular to the direction of the fork guide rails as well. An actuator (not shown) is positioned at a distal end of the drive shaft 315, and coupled thereto to drive the drive shaft for the gear shifting operation. Due to this perpendicular arrangement of the drive shaft 315 relative to the fork guide rails, the shifting device requires a relatively large volume, and it is generally difficult to reduce the size of the resultant transmission containing the shifting device.
In another example, U.S. Pat. No. 7,353,726 (assigned to ZF Friedrichshafen AG.) suggests a shifting device which has a structure generally similar to that described above with FIGS. 3a-3c. Similar to the above-described design, this gear shifting device also includes four gearshift frames of rectangular shape with cam grooves or recesses formed therein, multiple sets of sliding selector shafts affixed to the gearshift frames, and a shift drive shaft which extends in a direction perpendicular to the sliding selector shafts and with a plurality of shift fingers coupled thereto for engaging and disengaging operation of the gears. See FIG. 4 of U.S. Pat. No. 7,353,726.
As describes, this shifting device also requires complex cam parts to be precisely manufactured, such as four gearshift frames with cam grooves to be produced with high precision and accuracy, multiple shift fingers with precise cam contours. Thus, this shifting device also requires a complex production process and a high manufacturing cost. Moreover, as the shift drive shaft extends in a direction perpendicular to the sliding selector shafts, and also perpendicular to the direction of the fork guide rails as well. Accordingly, due to this perpendicular arrangement of the shift drive shaft relative to the fork guide rails, this shifting device also requires a relatively large volume, and it is generally difficult to reduce the size of the shifting device, and thus, the overall transmission as well.